1. Field of the Invention
This invention relates to a photographing apparatus such as a digital camera.
2. Description of the Related Art
Along with the progress of semiconductor techniques and image processing techniques, digital cameras are rapidly spreading in place of silver halide film cameras. In general, with a digital camera, an optical image formed by a photographing lens is photoelectrically converted into electric signals by image pick-up devices, such as CCDs (Charge Coupled Devices). The electric signals are subjected to image processing in order to generate image data, and the image data are stored in a recording medium, such as a memory card.
In recent years, a so-called single-lens reflex digital camera which uses the body of a silver halide single-lens reflex camera with which pictures are taken using silver halide films has been proposed. Such a single-lens reflex digital camera can make use of the resources of the silver halide single-lens reflex camera, and a CCD array is provided at a position of the film gate of the silver halide single-lens reflex camera.
Since the image quality of a digital camera is affected by the number of pixels of the image pick-up devices, it is desirable to use a large-sized CCD array having a number of pixels in order to guarantee the same level of image quality as the silver halide single-lens reflex camera. However it is difficult to manufacture a large-sized CCD array with a number of pixels, and the product yield would become very low.
To overcome this problem, it was proposed to incorporate three compact image pick-up devices in a digital camera, two of which are combined and used to artificially obtain luminance data from twice as many pixels as a conventional array, and the other one is a compact colour image pick-up device for obtaining colour information. However, this structure requires an optical system for splitting the optical path into the three image pick-up devices, and consequently, the size and the weight of the camera increase. In addition, it is difficult to adjust the optical axis with respect to the three image pick-up devices.
As another technique for a digital camera, a preview image is displayed on a display panel (e.g., as LCD panel) at a moving image data for checking the object.
However, if a plurality of image sensors are used, combined with the preview display technique, in order to increase the number of pixels, it requires time to read out the pixel signals from the image sensors, and the image updating rate becomes slow. If the image captured by the image sensors is used as a preview image as it is, the preview image cannot be displayed at the moving-image rate.
Therefore, it is an object of the present invention to overcome these problems in the prior art, and to provide a photographing apparatus which can produce pictures of high image quality without using a large-sized imaging device.
An another object of the present invention is to provide a photographing apparatus, which is small in size and light in weight and can facilitate adjustment of the optical axis, as compared with a photographing apparatus using a combination of three imaging devices.
Yet another object of the present invention is to provide a photographing apparatus which can display a preview image at a rate of a moving image, while a high-quality photographing image is achieved by using a combination of image sensors with an increased number of pixels.
In one aspect of the present invention, the object is achieved by a photographing apparatus which comprises a photographing lens, a first area sensor, a second area sensor, a display, a manipulation unit, and a processor. The first area sensor has a plurality of pixels, and photoelectrically converts an optical image of an object formed by the photographing lens into the first pixel data. The second area sensor has a plurality of pixels, the number of pixels of the second area sensor being greater than the number of pixels of the first area sensor, and photoelectrically converts an optical image of the object formed by the photographing lens into second pixel data. The first pixel data supplied from the first area sensor is displayed on the display unit as a preview image prior to image recording. The manipulation unit allows a user to begin image recording. The processor combines the first and second pixel data supplied from the first and second image sensors to produce a composite image when the manipulation unit is operated.
With this photographing apparatus, only two area sensors (i.e., the first and second area sensors) are used to produce a composite image. As a result, the size and the weight of the photographing apparatus can be kept small, as compared with a conventional photographing apparatus using a combination of three image sensors. In addition, it is easier to adjust the optical axis with respect to the two sensors, as compared with a triple-sensor type photographing apparatus.
Because the first pixel data supplied from the first area sensor, which has fewer pixels and is mainly used to generate a preview image, is combined with the second pixel data output from the second area sensor, which has more pixels than the first area sensor, in response to manipulation of the manipulation unit for starting image recording, a high-quality photographic image can be obtained without increasing the sizes of the respective area sensors.
Preferably, the first area sensor outputs colour information of the object, and the second area sensor outputs luminance information of the object.